Helicobacter pylori is a Gram negative bacillus which was isolated for the first time in 1982, and the presence of which in the organism has been associated with gastroduodenal diseases. More specifically, this bacillus is the main responsible for the development of duodenal peptic ulcer, as well as the main causative agent of chronic gastritis, where it appears in 90-95% of the patients, its presence also being detected in patients with duodenal ulcer, gastric ulcer, dyspepsia, gastric non-Hodgkin's lymphomas and even cases of gastric cancer.
With the object of establishing a proper and effective treatment of a possible gastroduodenal disease, it is necessary to carry out an accurate and reliable diagnosis of the same. Some methods for the diagnosis of gastroduodenal diseases are based upon the detection of Helicobacter pylori by methods that can be divided into invasive and non-invasive methods. Invasive methods require the performance of an endoscopy on the patient and the subsequent realisation of histological studies, cultures or the rapid urease test on samples of the gastric mucosa collected by endoscopic biopsy. Although these methods have an adequate sensitivity and specificity, they are expensive, they require trained personnel for carrying them out and produce discomfort to the patient who, occasionally, rejects them. Among the non-invasive methods it is possible to count the serological methods and the urea breath test. In general, the serological methods exhibit less sensitivity and specificity than the urea breath test and, additionally, only detect antibodies against H. pylori and not the presence of the same, as the .sup.13 C-labelled urea breath test does. The serological test is not reliable for monitoring the effectiveness of an eradicating treatment because a significant decrease in the antibody titre is appreciable after the sixth month post-eradication, without there being any certainty before the eighteenth month post-eradication, whereas, with the breath test it is possible to demonstrate with certainty the elimination of H. pylori by the treatment, starting from the first month after having concluded the same.
The urea breath test is based upon the fact that an abnormal urease activity is observed in numerous gastroduodenal diseases, particularly in those related with the presence of H. pylori, and hence, the detection of urease activity in abnormal amounts is indicative of the existence of H. pylori, and consequently, of a possible gastroduodenal pathology. Urease (urea amidohydrolase) is an enzyme which catalyses the hydrolysis of urea (carbonyldiamide) into ammonium carbonate which decomposes into carbon dioxide and ammonia. In order to carry out the urea breath test, the patient is administered urea, which is optionally labelled with carbon-13 (.sup.13 C), carbon-14 (.sup.14 C), or with nitrogen-15 (.sup.15 N), and the breath of the patient is subsequently analysed to detect the presence of products resulting from the hydrolysis of the labelled urea. The carbon dioxide labelled with carbon-13 or carbon-14, produced by the hydrolysis of the urea labelled with said isotopes, is absorbed by the blood system, transported to the lungs and is finally exhaled, making its detection possible in the breath of the patient.
The U.S. Pat. No. 4,830,010, held by B. J. Marshall, discloses a method for the diagnosis of gastroduodenal diseases based on the urea breath test, which presents numerous drawbacks, some of which are:
the use of solutions prior to the administration of urea which do not reproduce the pH in the stomachal antrum (between 2 and 2.3) which is suitable to maintain H. pylori in its environment, and, therefore, the results obtained are of dubious accuracy and reliability, and, additionally, these solutions often produce gastroduodenal disorders in the patient, such as diarrhoea, sensation of heaviness in the stomach, vomits, etc.; PA1 the use of urea labelled with carbon-14, a radioactive isotope, which increases the cost of the method and considerably limits its field of application, as it cannot be used on pregnant women or on children, not being it possible to repeat the test in the same patient more than two or three times due its radioactivity; PA1 the dosing of the labelled urea, as a function of the weight of the patient, entails a certain degree of complexity in carrying out the assay, as well as a greater consumption of the reagent with the consequent repercussions, not only at the economical level, but also in relation to the existence of a certain degree of risk due to toxicity and or adverse effects on the patient; PA1 the patient must remain in the horizontal position throughout all of the duration of the test, which can result in discomfort to the patient; and PA1 the collection of the patient's breath is carried out in plastic bags by the use of plastic mouth-pieces and subsequently the air is removed from the bags by the use of syringes and a Vacutainer.RTM. (a pressurised glass tube fitted with a rubber stopper, which on the long term may interfere with the gases produced from the air of the patient collected in the tube) is introduced. The large number of components necessary to collect the breath of the patient not only complicates the performance of the assay but also increases its cost, as in addition to the cost of the components, the cost of treating to the wastes generated, so as to avoid environmental problems, must be considered.
Consequently, the method described in the U.S. Pat. No. 4,830,010 is a general method, not very specific, and of dubious reliability and reproducibility, which has a limited field of application, is complex, expensive and a nuisance and a source of discomfort for the patient.
The present invention provides a method and a kit for carrying out a breath test with urea labelled with carbon-13, for the detection of H. pylori, which overcomes the disadvantages which where mentioned above. Particularly, the invention provides an assay for the detection of H. pylori which is simple, easy to conduct, reliable, reproducible, of wide application, uncomplicated, cost-effective, safe and comfortable for the patient.